Frasch process

The Frasch process is a process for extracting sulfur from sulfur-bearing calcite deposits, invented by Herman Frasch
in 1891. Three concentric pipes are lowered down a bore-hole to the ore.
Superheated water at 165°C is pumped down the outermost pipe and compressed
hot air is blown down the innermost pipe. This forces a frothy mixture of
molten sulfur up the middle pipe. Very pure sulfur is produced.